Point to Trusty instance via an environment variable

[jhrozek]

To make sure we're talking to the right trusty instance through the
k8s service name.

[jhrozek]

$ helm template just-a-test deployment/helm | grep -C 4 TRUSTY
walk.go:74: found symbolic link in path: /Users/jakub/devel/mediator/deployment/helm/config.yaml.example resolves to /Users/jakub/devel/mediator/config/config.yaml.example. Contents of linked file included and used
          - name: "MEDIATOR_AUTH_TOKEN_KEY"
            value: "/secrets/auth/token_key_passphrase"
          - name: "MEDIATOR_IDENTITY_SERVER_CLIENT_SECRET_FILE"
            value: "/secrets/identity/identity_client_secret"
          - name: "MEDIATOR_UNSTABLE_TRUSTY_ENDPOINT"
            value: "http://pi.pi:8000"

          # ko will always specify a digest, so we don't need to worry about
          # CRI image caching

[jhrozek]

and a test in cluster:

curl -v 'http://pi.pi:8000/pi/v1/report?package_name=urllib3&package_type=pypi' | head
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying 172.20.246.184:8000...
* Connected to pi.pi (172.20.246.184) port 8000 (#0)
> GET /pi/v1/report?package_name=urllib3&package_type=pypi HTTP/1.1
> Host: pi.pi:8000
> User-Agent: curl/7.76.1
> Accept: */*
>
  0     0    0     0    0     0      0      0 --:--:--  0:00:03 --:--:--     0* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< date: Thu, 02 Nov 2023 11:17:16 GMT
< server: uvicorn
< content-length: 8048
< content-type: application/json
<
{ [8048 bytes data]
100  8048  100  8048    0     0   2247      0  0:00:03  0:00:03 --:--:--  2246
* Connection #0 to host pi.pi left intact
{"package_name":"urllib3","package_type":"pypi","package_data":{"id":"e4ac84ae-e313-5c7a-bb73-b79a1e317721","status":"complete","status_code":null,"name":"urllib3","version":"2.0.6","author":"","author_email":"Andrey Petrov <andrey.petrov@shazow.net>","package_description":"\"\\n\\n![urllib3](https://github.com/urllib3/urllib3/raw/main/docs/_static/banner_github